This proposal describes a research program designed to determine the factors that contribute to the familial aggregation of specific language impairment (SLI). The first study proposed involves the collection of 40 extended family pedigrees for SLI to complement those gathered during the past project. Using these pedigrees, complex segregation analysis will be performed to determine whether there is a major genetic locus, as well as the extent to which genetic heterogeneity is present in these families. Also proposed is a twin study of SLI in which 50 pairs each of MZ and DZ twins will be studied. These data will be used to estimate the degree of genetic and environmental contributions to SLI as well as the penetrance of the genetic contribution to SLI. Within the twin study, will also be an investigation of the extent to which English morphological rule acquisition is strongly associated with genetic determinants. A third study is proposed that makes use of recent advances in genome mapping and linkage analysis. This study will look for genetic loci that are linked to the SLI phenotype in 125 affected sib-pairs. Finally we will study the reliability and diagnostic accuracy of a potential physiological phenotypic marker for SLI. Recently, averaged auditory evoked brain potentials to frequency modulated tones have been reported to be abnormal in SLI individuals with receptive language impairment. If this measure is found to be reliable and uniquely associated with SLI, it will provide a valuable physiological phenotypic marker for genetic studies of SLI. All of the research proposed is concerned with improving our understanding of the causes of a form of developmental language disorder in which the primary manifestation is one of the deficits in language development despite apparently normal auditory sensitivity and nonverbal intelligence. By determining the basis of this familial aggregation, improved early identification, and prevention may be possible.